The 16-year-old stars in a feature for Teen Vogue's April issue, modelling Alexander McQueen, Topshop and Chanel — all designers that big sister Kate has good relationships with.
The teenager expressed her delight at her first modelling job in an accompanying interview. "Teen Vogue is my first proper job! I'd really like to work at Teen Vogue," she said.
Asked why she wanted to model, Lottie explained it was Kate's influence. "Well, it kind of runs in the family," she said. "Kate was a massive part of why I started."
She appears to share her half-sister's love of fashion, too. "My dream would be to have all [Christian Louboutin] shoes," she admitted.
"But I can't afford any because I don't have a job, and I can't make my parents pay for that."
Lottie was signed to Storm Model Management earlier this year. It is the same modelling agency that Kate started out at the age of 14 with and has guided her supermodel career ever since.
Lottie's potential as a model was first spotted when she appeared as a bridesmaid at Kate's 2011 wedding . However, as she was just 13 at the time, she wasn't allowed to be signed up to an agency and settled with test shoots with Storm.
Her signing was officially announced on the day she turned 16.
The teenager took to Twitter to proudly announce her news, posting a picture of her portfolio page on the Storm website. "Wot u sayin," she captioned the snap.
Storm then tweeted a close-up picture of Lottie, with "Happy Birthday Lottie, Love Storm" written across it in pink font.
Appearing in the agency's 'New Faces' section, the portfolio features 13 black and white photographs of Lottie. It also lists her height as 5'5", an inch smaller than her elder sister.
Watch the Unique Topshop Women's Fall/Winter 2014/15 Collection in London